The Ninth Circuit Court of Appeals ruled Friday in United States vs. Forester that IP addresses and the To/From fields in emails are the legal equivalent of dialed phone numbers and the government can get a court order to obtain them without showing probable cause as would be needed in a search one’s house.

The Court extended to the internet a 1979 case known as Smith vs. Maryland, where the Supreme Court found that individuals have no reasonable expectation of privacy in the phone numbers they dial because they transmitted them to the phone company in order to complete the call. However, under Smith, the contents of the calls could not be listened in on without proving probable cause to a judge.

The Ninth Circuit, ruling in an appeal of an Ecstasy-drug ring conviction found that emails’ To/From fields and visited IP addresses were the internet’s equivalent of phone numbers. For example, the government could get a log that said a person visited to http://66.230.200.100 (Wikipedia’s address). However, the court suggested that knowing full urls are very close to content (e.g. http://en.wikipedia.org/wiki/Ecstasy) and would likely require a higher burden of proof to obtain than mere IP addresses.

From a footnote in the decision:

Surveillance techniques that enable the government to determine not only the IP addresses that a person accesses but also the uniform resource locators (URL) of the pages visited might be more constitutionally problematic. A URL, unlike an IP address, identifies the particular document within a website that a person views and thus reveals much more information about the personþs Internet activity. For instance, a surveillance technique that captures IP addresses would show only that a person visited the New York Times’ website at http://www.nytimes.com, whereas a technique that captures URLs would also divulge the particular articles the person viewed.

Professor Orin Kerr questions whether the decision is about getting this information from an ISP or whether it was from a device installed on a computer surreptitiously. He suggests the latter should require a higher standard, but I’m not sure why? Perhaps it’s because that might require law enforcement to enter a person’s house?